Hairspring and balance arm assembly



April 19, 1955 B. E. WOLFE 2,706,381

HAIRSPRING AND BALANCE ARM ASSEMBLY Filed June 24, 1955 pie/0e 19.87

INVENTOR BRUCE a. WOLFE ATTORNEY United States Patent HAIRSPRHNG ANDBALANCE ARM ASSEMBLY Bruce E. Wolfe, Landisville, Pa., assignor toHamilton Watch Company, Lancaster, Pa.

Application June 24, 1953, Serial No. 363,741 4 Claims. (Cl. 58-115)This invention relates to an and balance arm assemblies.

In time fuses and mechanisms of a like type where an oscillating balancearm and hairspring assembly is used to regulate the escapement of power,a pivoted staff having an arm and a hairspring is used. It hasheretofore been the custom to drill a round hole slightly off center inthe staff and to insert the hairspring and pin the same by a straightpin in the hole. This produces a hairspring with a curved crosssectional area which has a tendency to flex more in one direction thanthe other and to break.

It is the object of the present invention to provide the method ofmanufacture of the staff so that the hairspring may be mounted in thestaff without any distortion whatsoever.

It is a further object of the present invention to proyide a means formaking a recess in the hole in the staff to receive the hairspring stripand to hold the same without distortion.

The invention is shown in the accompanying drawing in which:

Figure 1 is a perspective view showing the complete balance arm andhairspring assembly as in use today.

Figure 2 is an enlarged detail of the staff.

Figure 3 is a perspective view of the balance arm and hairspringassembly with the added improvement.

Figure 4 is an enlarged detail view of the staff.

Referring first to Figures 1 and 2, a staff 9 is shown having upperpivot 10 and lower pivot 11. A collar 12 receives the balance arm 13While the staff is bored at right angles to its longitudinal length andslightly off center, as at 14, so as to locate the hairspring 15substantially in a plane passing through the longitudinal axis which maybe termed the longitudinal center of the staff. The hairspring 15 ispinned in position by a tapered pin 16 which Wedges the hairspringagainst the curved side of the opening 14 and distorts the hairspringinto the shape shown in Figure 2. This curve along its longitudinallength makes the hairspring flex unequally in different directions andin some cases causes breakage before the timing mechanism has fulfilledits purpose.

Referring particularly to Figures 3 and 4 in which the change ofconstruction and new method of making and assembling the balance arm andhairspring assembly is shown, a very similar balance arm 17 is mountedon a staff 18 having pivots 19 and 20 and a central face portion 21. Theoff center hole 22 in the face 21 is drilled improvement in hairspringsimilarly to the hole 14 but an additional operation consisting of usinga shaving tool forms a groove 23 on opposite sides of the hole. Thegroove 23 is rectangular in cross section and the same size as thehairspring 24 which it snugly receives and holds in a flat undistortedposition. A straight pin 25 similar to pin 16 is then drawn through thehole and by wedging the hairspring against the sides of the groove 23securely holds it in position. This hairspring 23 is capable of flexingequally in either direction and by reason of being free of anydistortion is very unlikely to break before the function of the timingdevice is fulfilled.

What is claimed is:

1. A balance arm and hairspring assembly, comprising a staff mounted foroscillation, a balance arm attached to said staff, said staff beingformed with a transverse hole having opposite parallel grooves, ahairspring receivable in the hole and seated in one of the grooves and atapered pin receivable in said hole to securely lock said hairspring insaid groove without any distortion of said hairspring.

2. A balance arm and hairspring assembly, comprising a staff mounted foroscillation, a balance arm attached to said staff, a hairspring, saidstaff being formed with a transverse hole having opposite parallelgrooves of a depth equal to the thickness of the hairspring, saidhairspring being receivable in the hole and seated in one of saidgrooves, and means for securing the hairspring in desired positionwithout distorting the hairspring.

3. A balance arm and hairspring assembly, comprising a staff mounted foroscillation, a balance arm attached to the lower half of said staff, theupper half of said staff being formed with parallel flattened portions,said fiattened portions having a transverse hole formed with a pair ofopposite parallel grooves, one of said grooves being along thelongitudinal center of said balance staff, a hairspring equal inthickness to the depth of said groove receivable in said hole and seatedwithin the groove along the longitudinal center line, and a pin engagingthe hairspring and wall of said hole for securely holding said spring inposition without any distortion of said spring.

4. A balance arm and hairspring assembly, comprising a staff mounted foroscillation, a balance arm attached to the lower half of said staff, theupper half of said staff being formed with parallel flattened portions,said flattened portions having a transverse hole formed with alongitudinal groove, said groove being along the longitudinal center ofsaid balance staff, a hairspring equal in thickness to the depth of saidgroove receivable in said hole and seated within the groove along thelongitudinal center line, and a pin engaging the hairspring and wall ofsaid hole for securely holding said spring in position without anydistortion of said spring.

References Cited in the file of this patent UNITED STATES PATENTS1,556,907 Bold Oct. 13, 1925 FOREIGN PATENTS 745,242 France Feb. 14,1933

